The importance of chain terminating or end-capping copolyester-carbonate resins by means of certain molecular weight regulating or chain terminating compounds is well known in the art. Copolyester-carbonates which are not end-capped or chain terminated are generally insufficiently heat stable. Furthermore, the absence of chain terminating or end capping agents or conditions during the preparation of the aromatic copolyester-carbonates results in polymers with a molecular weight which is often so high that the polymers are too viscous to mold at reasonable temperatures.
Standard chain terminating agents employed in the preparation of copolyester-carbonate resins include members of the phenol family such as phenol itself and tertiarybutyl phenol. While these phenol chain terminating agents are generally effective, there is a need, in certain applications, for copolyester-carbonate resins exhibiting higher terminal stabilities than those exhibited by conventional copolyester-carbonates employing phenols as end capping agents. It is known that replacing these phenol end capping agents by benzoate esters yields copolyester-carbonates exhibiting improved heat resistances.
However, the field of chain terminators and their effects upon the properties of copolyester-carbonates is generally not completely understood and is one wherein the empirical approach is generally the rule rather than the exception in determining whether a particular compound or class of compounds will function effectively as chain terminators. Thus, for example, while a particular compound may function effectively as a chain terminator another similar compound may be ineffective as a chain terminator. This area is further complicated by the fact that not only must a particular compound function as a chain terminator, but this compound when incorporated into the copolyester-carbonate polymer as a terminal group must not adversely affect the positive and advantageous properties of the copolyester-carbonate. Thus, while some compounds may be effective chain terminators they may not be practical since they have an adverse effect upon the advantageous mechanical and physical properties of the copolyester-carbonate resins.
It is an object of the instant invention to provide novel amide and carbamate chain terminated copolyester-carbonates exhibiting improved thermal stabilities.